In one example of a prior art well tool, a bridge plug carried on the end of the tubing string may be anchored to the casing of the well in a selected downhole position to isolate the zone in the well below the tool from the zone above the tool for the performance of a well service operation, such as acidizing, formation fracturing or pressure containment. Because a particular well may require that such operations be carried out at different locations within the well, it is desirable that the tool have the ability to be moved from location to location without having to pull the tubing string from the well to redress the tool. In one form of bridge plug currently available, a tubular mandrel is connected to the lower end of the tubing string and mounted on the mandrel is a slip assembly and sealing unit. Connected to the slip assembly is an anchor cage or reaction member which typically engages the inside surface of the casing so that relative motion between the slip assembly and the mandrel may be obtained by manipulation of tubing string. Typically, the manipulation of the tubing string includes both rotational movement in clockwise and counterclockwise directions as well as movement axially relative to the casing in either direction within the well. Combinations of rotational or axial movement may be utilized in the tool to cause slips in the slip assembly to be set against the well casing to anchor the tool in a selected position, and also to release the tool from that position for subsequent resetting at another location.
In another type of well tool, the wireline retrievable bridge plug, the tool may be lowered into position in the well on a wireline and set, such as by means of a wireline setting gun. The wireline tool, however, lacks the ability to be released and reset within the well without having to be pulled from the well for redressing purposes. However, advantages do exist in that lighter duty equipment may be used at the well head for conducting wireline operations as opposed to heavy duty workover rigs or production rigs that are necessary to provide support for the heavier well tubing.